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A comparison of the efficiencies of bromates and nitrates in the separation of the rare earth elements… Wylie, Dorothy Elinore 1933

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•A. COMPARISON. OF .THE EFFICIENCIES OF BROMATES AND NITRATES IN THE SEPARATION OF THE RARE EARTH ELEMENTS FROM ONE ANOTHER • • ' by Dorothy S l i n o r e Wylie o o o o o -A; :THES IS; SUBWITIED FOR TEE DEGREE OF M A S T E R OF APR T S. IN.THE DEPARTMENT C H E M I S T R Y o o o o o o THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1952 TABLE OF CONTENTS.. A. I n t r o d u c t i o n . Page 1 B. H i s t o r i c a l . . . Page 2 C. Experimental Page 5 D. Pr e p a r a t i o n of the S a l t s . . . . . Page. 7 Se r i e s A.A. N i t r a t e s > Page 7 Se r i e s B.B. Bromates. Page 7 E. Pr e p a r a t i o n of Samples . . > Page 9 F. D i s c u s s i o n of R e s u l t s . Page 11 G. Summary Page 13. P l a t e I Page 15 (1) A COMPARISON OF THE EFFICIENCIES  OF 3R0MATES AND NITRATES IN THE SEPARATION OF THE RARE EARTH ELEMENTS FROM ONE ANOTHER» A. INTRODUCTION: Increased i n t e r e s t i s being taken i n the elements of the Rare Earth Group Owing to t h e i r growing impor-tance i n i n d u s t r y and t o the f a c t that they o f f e r i n t e r e s t -ing s t u d i e s from the viewpoint of atomic s t r u c t u r e , o r i g i n e t c . In every case, however, progress i s retarded owing to the extreme d i f f i c u l t y w i t h which, they may be separated from one another. The i s o l a t i o n or i d e n t i f i c a t i o n of the i n d i v i d u a l jse&ibers of t h i s group covers a period ox some'130 years, the f i r s t member being discovered i n 17S4 whereas the existence of the l a s t was only demon-s t r a t e d i n 1926. During t h i s period a great many methods have been used f o r the s e p a r a t i o n and p u r i f i c a t i o n of the elements, methods i n v o l v i n g i n the main part d i f f e r e n c e s i n the s o l u b i l i t i e s of simple or double s a l t s of the elements, or d i f f e r e n c e s i n the b a s i c i t i e s of the oxides. As a r e s u l t the i n d i v i d u a l members of the e n t i r e group have been i s o l a t e d i n s u f f i c i e n t amounts to allo w of t h e i r i d e n t i f i c a t i o n as elements, even though very few have 1. H a r r i s with H o p k i n s — J .A. C-S. > 48, 1586. (2). been prepared i n . a s t a t e 02 atomic p u r i t y i n any q u a n t i t y , and these only a f t e r extensive f r a c t i o n a l c r y s t a l l i s a t i o n s . The methods used, have n a t u r a l l y v a r i e d w i t h each i n v e s t i g a t o r and as a r e s u l t the l i t e r a t u r e i s f i l l e d w i t h c o n f l i c t i n g statements as to the r e l a t i v e s o l u b i l i t i e s , e t c . , and whereas.separation of the elements has been ac-complished by v a r i o u s means, there i s no c l a i m rcade as t o the method used being the most e f f i c i e n t one. The r e s u l t has been therefore t o use f o r p r e l i m i n a r y s e p a r a t i o n s , methods that have been shown t o be f a i r l y s u c c e s s f u l , and the general separations the f i n a l p u r i f i c a t i o n g e n e r a l l y depends 011 the person who i s working on the p a r t i c u l a r problem* B. _ HISTORICAL: D u r i n g the concentration of i l l i n i u m i t was obvious that although a great' d e a l of data was a v a i l a b l e regarding methods f o r producing a s e p a r a t i o n of the rare e a r t h e l -ements from one another, any t h i n g i n the way of a compar-a t i v e study o f these methods was l a c k i n g * P r e l i m i n a r y s e p a r a t i o n of cerium group earths i s g e n e r a l l y accomplished by the f r a c t i o n a l c r y s t a l l i z a t i o n of a double s a l t , u s u a l l y the double magnesium n i t r a t e . I n the case o f the yttrium.group earths, f r a c t i o n a t i o n of the bromates appears to be the method most f r e q u e n t l y used (5) although the simple n i t r a t e s have a l s o been recommended. Our or;n i n t e r e s t , as has been pointed out i n previous papers, i s d i r e c t e d c h i e f l y towards t h e f i n d i n g of a more e f f i c i e n t method f o r the concentration of i l l i n i u m than was used f o r i t s i s o l a t i o n . Consequently our e f f o r t s have been d i r e c t e d towards a comparative study of the e f f e c t of c r y s t a l . l i z i n g as many d i f f e r e n t s a l t s as p o s s i b l e i n the hope t h a t some one s a l t might prove Eore e f f e c t i v e i n per-m i t t i n g of a concentration of a p a r t i c u l a r element than the others. In every case therefore i d e n t i c a l m a t e r i a l was used, and the cond i t i o n s of c r y s t a l l i z a t i o n maintained as n e a r l y the same i n a l l cases as p o s s i b l e . The e f f e c t of the f r a c t i o n a t i o n was i n each case observed by com-paring t h e a b s o r p t i o n s p e c t r a of s o l u t i o n s made up from a d e f i n i t e volume of saturated s o l u t i o n from each f r a c t i o n . The r e s u l t s from such a study of t h e spectra obtained from v a r i o u s s e r i e s of s a l t s o f the--cerium group earths have 2 2,5. been re p o r t e d , and i t was p o s s i b l e from such a comparative study.-to note that c e r t a i n s a l t s a r e more e f f e c t i v e i n b r i n g i n g about a r a p i d separation of c e r t a i n elements than are the others. Consequently a great d e a l of time may be saved by s e l e c t i n g the s a l t to be used, f o r p r e l i m i n a r y separation as c a r e f u l l y as that f o r the f i n a l p u r i f i c a t i o n . A s i m i l a r i n v e s t i g a t i o n as t o the r e l a t i v e e f f e c t s 2. Pearce with H a r r i s — T . R . S - C > Sec. I l l , 1930, 145. 3, Wylie -vi'th H a r r i s — T . R . S . C , Sec. I l l , 1951, 107. (4) of the f r a c t i o n a l c r y s t a l l i z a t i o n of s a l t s of the r a r e e a r t h s obtained, from g a d o l i n i t e was c a r r i e d out. The s a l t s u sed were the s i m p l e n i t r a t e s and the bromates as these have proved more e f f e c t i v e i n the separation of the y t t r i u m group e a r t h s . The f r a c t i o n a l c r y s t a l l i z a t i o n of the bromates was i n t r o d u c e d by James i n h i s c l a s s i c a l work on the y t t r i u m group earths. I n .'his l a t e r paper on the "Separation of the Rare E a r t h s B he sugges.ts f o u r d i f f e r e n t methods f o r a t t a c k i n g the crude o x a l a t e s , depending on the c o n c e n t r a t i o n of the l a t t e r . F o r the separation of the crude y t t r i u m earths he recommends the f r a c t i o n a l c r y s t a l l i s a t i o n of the bromates. He c o n v e r t e d the oxalates t o t h e anhydrous s u l p h a t e s by t r e a t i n g them w i t h a s l i g h t .excess of s u l -p h u r i c a c i d and h e a t i n g u n t i l a l l l u s e s o f s u l p h u r i c a c i d c eased t o be e v o l v e d . The i g n i t e d s u l p h a t e s were d i s s o l v e d i n c o l d water and a f a i r l y s t r o n g s o l u t i o n of them were . added t o b a r i u m bromate, covered w i t h a l a y e r of water and h e a t e d on a steam b a t h . The whole was f i l t e r e d when decom-p o s i t i o n was completed and the b a r i u m s u l p h a t e w e l l washed w i t h hot water-* The c l e a r l i q u i d was e v a p o r a t e d u n t i l c r y s t a l s formed and the..mother l i q u o r and c r y s t a l s were f r a c t i o n a l l y c r y s t a l l i s e d . . • -U s i n g t h i s method James found that'Samarium and 4, G. James—J.A. C-S. , 1208, 50,182.; 1912, 34,757. <6> GafioliEium r a p i d l y s e p a r a t e d i n t h e l e a s t s o l u b l e c r y s t a l s , * f o l l o w e d by Dysprosium, Holmium and Y t t r i u m , whereas the most s o l u b l e f r a c t i o n s c o n t a i n e d p r a c t i c a l l y pure Erbium, This method has been used e x t e n s i v e l y since by r a r e e a r t h w o r k e r s i n the Y t t r i u m group-. F r a c t i o n a l c r y s t a l l i z a t i o n of t h e n i t r a t e s was . -6., . f i r s t used by Dewarcay who found that t h i s method was p a r t i c u l a r l y e f f e c t i v e when the mixture of e a r t h s con-t a i n e d no element of a t o m i c weight l e s s t h a n that of d^rpsiuBU , Baur and Marc found t h e method very e f -f i c i e n t f o r sepa r a t i n g g a d o l i n i u m from y t t r i u m and i t has s i n c e been u s e d e x t e n s i v e l y by U r b a i n and o t h e r s . Q. • EXPEHIKSITAL::-. S t a r t i n g w i t h t h e crude o r e , t h e r a r e e a r t h s were e x t r a c t e d and a f t e r p u r i f i c a t i o n samples of these were t a k e n and converged i n t o bromates and n i t r a t e s . F r a c t i o n a l c r y s t a l l i z a t i o n o f the two s e r i e s was c a r r i e d out i n o r d e r t o determine-which.salt brought about the b e t t e r s e p a r a t i o n o f members o f .the y t t r i u m group. The m a t e r i a l used had i t s source i n Norwegian Gadolinit-e. The e a r t h s were 'extracted w i t h h y d r o c h l o r i c a c i d o r c o n c e n t r a t e d sodium h y d r o x i d e f o l l o w e d by n i t r i c a c i d e x t r a c t i o n , these '-extract&nts h a v i n g been shown t o be . . . 7, the 'most e f f i c i e n t ones f o r t h i s m i n e r a l . Thife: l i q u o r 6v Bernarcy.y—Cozra?. Bend., 1896, 122, 728.-6, Baur & M a r c — B e r . , 1901, 54, 2460. 7. Horn's-Peorce ~T.H.S-C". s S e c I I I , 1929 , 61. (6) containing the earths was then d i l u t e d , and the earths p r e c i p i t a t e d .as the hydroxides by ammonia. • The mixture was f i l t e r e d , washed- thoroughly, and then taken i n t o s o l u t i o n i n the Biinirsim amount of n i t r i c a c i d . The r e s u l t i n g s o l u t i o n was d i l u t e d , heated, and the oxalates p r e c i p i t a t e d by the a d d i t i o n of excess of satu r a t e d o x a l i c a c i d s o l u t i o n . These were f i l t e r e d , washed s e v e r a l times with water and again f i l t e r e d , d r i e d and i g n i t e d to the oxides i n a muffle. Since the presence of cerium renders the prep-a r a t i o n of the torornate d i f f i c u l t , owing to the a c i d character of s o l u t i o n s of cerium sulphate, i t i s necessary to remove even the small amounts of cerium which are present i n gudolinit-e* The oxides were extracted with n i t r i c a c i d c o n t a i n i n g a l i t t l e hydrogen peroxide and the small amounts of i n s o l u b l e m a t e r i a l f i l t e r e d out. The f i l t r a t e was d i l u t e d to s e v e r a l tiroes i t s o r i g i n a l volume and brought to n e u t r a l i t y by the a d d i t i o n of ammonia. Marble ships and s o l i d potassium b r ornate were no?; added and the s o l u t i o n brought to b o i l i n g . A f t e r allowing.the mixture to c o o l j the b a s i c cerium was f i l t e r e d out and the earths i n the s o l u t i o n p r e c i p i t a t e d as the hydroxides with •ammonia* • ..• -These were washed thoroughly by decantation and then d i s s o l v e d i n n i t r i c a c i d * The s o l u t i o n was then evaporated u n t i l the n i t r a t e s c r y s t a l l i z e d out followed by t h e i r s o l u t i o n i n r/ater unci the p r e c i p i t a t i o n of the earths as oxalates w i t h subsequent i g n i t i o n to the oxides. De -PREPARATION OF THE SALTS.. Samples of the p u r i f i e d oxides weighing 250 grams were • taken i n each case-, •SERIES .A.A. NITRATES-. The oxides were moistened with water and then warmed with concentrated n i t r i c a c i d u n t i l s o l u t i o n was e f f e c t e d . The s o l u t i o n was t h e n evaporated u n t i l c r y s -t a l l i z a t i o n was almost complete upon c o o l i n g to room temperature. The s a l t was then c r y s t a l l i z e d from con-centrated n i t r i c a c i d u n t i l a s e r i e s of eight f r a c t i o n s had been b u i l t up s new f r a c t i o n s being s t a r t e d w i t h s i x t h , eleventh., s i x t e e n t h , twenty-fourth, f o r t y second and f i f t i e t h pourings, making a t o t a l of f i f t y - t w o c r y s t a l -l i z a t i o n s i n the case of f r a c t i o n one, cold two i n the case of f r a c t i o n seven. .-. ~ SF;RIPS B.B. BROMATES. - - 8-, I n a paper published by H a r r i s i t was pointed out that the c l a s s i c a l method f o r t h e preparation of the bromates i s that of James. I t was a l s o shown how-e v e r , that d i f f i c u l t y is/encountered when t h i s method i s used f o r t h e preparation of the bromates of the cerium 8. J.A.CS, , 53, 2475, 1951*. (8). group e a r t h s s when larg e amounts o f the more b a s i c members a r e p r e s e n t . At t h e same t i m e the method i n v o l -v i n g as i t does t h e d e c o m p o s i t i o n of the s u l p h a t e r a d i c a l by the o x a l a t e i o n , I s o b j e c t i o n a b l e f r o m the s t a n d p o i n t c f the c o p i o u s e v o l u t i o n of fumes > and t h e n e c e s s i t y f o r .the s o l u t i o n o f t h e r e s u l t i n g s u l p h a t e s i n I c e water* The method by H a r r i s e l i m i n a t e d these o b j e c t i o n a b l e f e a t u r e s s and so i t was deemed a d v i s a b l e t o attempt t o a p p l y i t to t h e y t t r i u m group e a r t h s . The second sample o f o x i d e s was moistened .with water t o a l l o w o f r e a d y p e n e t r a t i o n by t h e a c i d and. the n t r e a t e d - w i t h s m a l l p o r t i o n s of s u l p h u r i c a c i d (1:5)' a l -l o w i n g the l i q u o r to reach n e u t r a l i t y b e f o r e subsequent a d d i t i o n of a c i d , i l l en the p o i n t had been reached a t which t h e l i q u o r remained acid., the m i x t u r e was gen t l y h e a t e d u n t i l n e u t r a l i t y was a g a i n a t t a i n e d . ' The a d d i t i o n of a c i d ?;as then c a r r i e d out on a hot p l a t e u n t i l a f a i n t l y a c i d s o l u t i o n p e r s i s t e d . When such a c o n d i t i o n was reached t h e m i x t u r e was e v a p o r a t e d t o d r y n e s s . When dry, the sulphates were removed and p u l v e r i s e d , and i g n i t e d i n s m a l l p o r t i o n s w i t h f r e q u e n t s t i r r i n g o v e r a s t r o n g f l a m e u n t i l a l l e x c e s s a c i d had been removed and t h e anhydrous s a l t o b t a i n e d . T h i s v/as q u i c k l y t r a n s f e r r e d t o a d r y , p r e v i o u s l y weighed c o n t a i n e r , r o u g h l y weighed and t r a n s -•ferred i m m e d i a t e l y while s t i l l h ot t o a b e l l j a r which was e v a c u a t e d . Froia t h e weight of the sulphates' the amount o f water n e c e s s a r y f o r t h e i r s o l u t i o n was c a l c u l a t e d and measured i n t o a l a r g e b e a k e r , f h e n c o o l the s u l p h a t e s were removed i n s m a l l p o r t i o n s and s p r i n k l e d w i t h v i g -orous s t i r r i n g i n t o t he w a t e r where t h e y d i s s o l v e d f a i r l y r e a d i l y g i v i n g a s o l u t i o n n e u t r a l to l i t m u s . A s a t u r a t e d s o l u t i o n o f b a r i u m bromate'was • pre-pared | the s u l p h a t e was added t o t h i s i n s m a l l p o r t i o n s making s u r e t h e r e was always an excess of b a r i u m i o n i n s o l u t i o n and the s o l u t i o n was k e p t a t 100° and s t i r r e d m e c h a n i c a l l y . When a l l t h e s u l p h a t e s o l u t i o n was added, t h e barium s u l p h a t e p r e c i p i t a t e was f i l t e r e d o u t . The s o l u t i o n o f r a r e e a r t h b r o i s a t e s thus o b t a i n e d was e v a p o r a t e d s l o w l y on a steam b a t h u n t i l c r y s t a l s formed, t h e n t h e bromates were p l a c e d i n the c o l d and a l l o w e d to • c r y s t a l l i z e - . -F*- PREPARATION -OF SAMPLES: As was r e p o r t e d i n nrevicus p a p e r s , i n o r d e r t o compare t h e r e l a t i v e s e p a r a t i o n s over the e n t i r e s e r i e s a t the f i n a l cr y s t a 11 i za t i o n and t o a s c e r t a i n i f p o s s i b l e the r e l a t i v e amounts o f the v a r i o u s e a r t h s i n each f r a c -tio-n, - ea-ch- s e r i e s was t a k e n and a c i d o r wa t e r added t o the f r a c t i o n s and r e c r y s t a l l i s a t i o n e f f e c t e d so t h a t t h e ' volumes of l i q u o r and c r y s t a l s were approximately the same. Since the a c i d r a d i c a l has a marked e f f e c t on the a b s o r p t i o n spec t r a of rare earth s o l u t i o n s I t was deemed • a d v i s a b l e to convert the s a l t s i n each case to the n i t r a t e s f o r s p e c t r o s c o p i c examination. The I n d i v i d u a l f r a c t i o n s of the two s e r i e s were ther e f o r e maintained at constant temperature f o r several hours i n order to permit of e q u i l i b r i u m between the s o l i d and l i q u i d being reached. 10 c. c. samples of the saturated s o l u t i o n s were then withdrawn, t r a n s f e r r e d t o l a r g e beakers and eva-porated to dryness. The r e s i d u e s were taken up i n water and the earths p r e c i p i t a t e d as the hydroxides by means of ammonia. The p r e c i p i t a t e s were washed wit h water, d i s s o l v e d i n a l i t t l e n i t r i c a c i d , the s o l u t i o n d i l u t e d and the r a r e earth oxalates p r e c i p i t a t e d from hot s o l -u t i o n by means of o x a l i c a c i d . These were th en i g n i t e d t o the oxides. The oxides a f t e r weighing,: : f o r reference purposes, \?ere moistened with a l i t t l e water and- d i s s o l v e d i n concentrated n i t r i c a c i d and evaporated to dryness« They were.taken up In water containing a l i t t l e hydrogen -peroxide and evaporated s e v e r a l times to expel 1 a c i d . 5 c c . of d i s t i l l e d water were added to each d r i e d sample . and warmed s l i g h t l y to e f f e c t s o l u t i o n . Except i n the cases of f r a c t i o n s seven and e i g h t of the n i t r a t e s e r i e s , c l e a r s o l u t i o n s were obtained. In 'these samples, however* ( I I ) a b c s i c s a l t p r e c i p i t a t e d and was f i l t e r e d out. Con-s e q u e n t l y w i t h t h e e x c e p t i o n of t h e s e two f r a c t i o n s , each sample r e p r e s e n t e d t h e amount o f r a r e e a r t h s c o n t a i n e d i n 10 c c o f the o r i g i n a l s a l t s o l u t i o n and now c o n t a i n e d i n 5 c«o. o f s o l u t i o n as the n i t r a t e . The s o l u t i o n s were photographed t h r o u g h a 5 e r a . c e l l . The a b s o r p t i o n bands r e c o r d e d were compared t o t h e spectrum of a s t a n d a r d i r o n a r c , and a l 3 o t o the a b s o r p t i o n o b t a i n e d from s t a n d a r d s o l u t i o n s of neodysiura, samarium, e r b i u m and h o i Mum., photographed t h r o u g h the same c e l l . P. DISCUSSION OP RESULTS: The photographs o b t a i n e d f rom t h e s o l u t i o n s d i s -c u s s e d above a r e r e p r o d u c e d i n P l a t e I . An i t e r p r e t a t i o n of these a b s o r p t i o n s p e c t r a i s e g r e c o m p l i c a t e d t h a n i n t h e case of a s e r i e s composed of elements of the cerium group a l o n e . In the s e r i e s d i s c u s s e d i n t h i s paper, i n a d d i t i o n t o h a v i n g members of the y t t r i u m group e a r t h s p r e s e n t s m a l l amounts of cerium group elements a r e p r e s e n t c a u s i n g o v e r l a p p i n g o f a b s o r p t i o n bands. L i k e w i s e , s e v -e r a l members of the y t t r i u m group e a r t h s y i e l d s o l u t i o n s t h a t have b u t l i t t l e or no a b s o r p t i o n i n t h e v i s i b l e r e g i o n of the spectrum. I t th u s i s p o s s i b l e at t h i s s t a g e t o o b t a i n o n l y a g e n e r a l i d e a as t o the r e l a t i v e ' e f f e c t i v e n e s s of each s a l t i n --reducing s e p a r a t i o n s of i n d i v i d u a l members of the r a r e earth group. (IB) e om The s o l u t i o n s of the bromates v a r i e d i n colour f r o m c o l o r l e s s i n t h e f i r s t f r a c t i o n , to a d a r k p i n k i n the t h i r d one, f a d i n g away t o a v e r y p a l e t i n t I n t h l a s t two. The o x a l a t e s f r om f r a c t i o n 1 were white s f r 2 and 3, p ink, from 4 and 5. white . and f r o m S, ? and 8 pink, •The a b s o r p t i o n s p e c t r a - i n d i c a t e s t h a t t h e r e i s a r a p i d c o n c e n t r a t i o n of neodymium and samarium-in the head f r a c t i o n s , whereas the erbium c o n c e n t r a t e s i n t h e l e a s t s o l u b l e f r a c t i o n s . A p r e l i m i n a r y s t u d y of ab-s o r p t i o n bands would i n d i c a t e the c o n c e n t r a t i o n o f Europium i n F r a c t i o n 1, Samarium, Terbium and Needy nil urn i n F r a c t i o n s 2 and 3, Dysprosium i n F r a c t i o n 4,•fiolmium i n F r a c t i o n 5, a c o l o u r l e s s e a r t h ( p o s s i b l y y t t r i u m ) : i n F r a c t i o n 8 and E r b i u m i n F r a c t i o n s ? and 8. The bromates would appear t o be o f most use i n s e parating Neodymium and Samarium from Eolmiuin, Y t t r i u m and E r b ium i n a p r e l i m i n a r y f r a c t i o n a t i o n of a s e r i e s c o n t a i n i n g a l l of the Y t t r i u m Group e a r t h s t o g e t h e r w i t h some of the cerium Group. The f i n a l s o l u t i o n s f r o m the n i t r a t e s v a r i e d f r o m a l m o s t c o l o u r l e s s i n F r a c t i o n 1 t o a deep p i n k i n F r a c t i o n 5. F r a c t i o n 6 showed a s l i g h t orange colour,. F r a c t i o n ? a -deep orange, and F r a c t i o n 8 a deep y e l l o w c o l o u r . In photographing the a b s o r p t i o n S p e c t r a ' o f these solutionis (IS); i t was i m p o s s i b l e t o o b t a i n ixnif or.; i n t e n s i t y i n the l a s t t h r e e f r a c t i o n s owing t o t o t a l a b s o r p t i o n f r o m y e l l o w t o v i o l e t . I n the photographs produced, the l&wer f i g u r e r e p r e s e n t s the r e s u l t s o b t a i n e d b y p r o l o n g e d e x -posure of t h e t h r e e l o w e r f r a c t i o n s . The i n t e n s i t y of t h e bands i n th e s e cases cannot t h e r e f o r e be used f o r c o m p a r i s i o n w i t h t h e o t h e r exposure-??,. The n i t r a t e s b r i n g about a t o t a l l y d i f f e r e n t o r d e r o r s e p u r a t i o n t o t h a t produced b y the f r a c t i o n a l c r y s t a l l i z a t i o n of t h e bromates. Terbium, Europium, Dysprosium and Samarium appear t o concentrate i n t h e head f r a c t i o n s f o l l o w e d b y Holroiuia, E r b i u m and f i n a l l y Neo-dyaiium, a l t h o u g h i t i s d i f f i c u l t t o i n t e r p r e t the S p e c t r a of t h e l a s t t h r e e f r a c t i o n s as i n d i c a t e d p r e v i o u s l y . The v a l u e of the n i t r a t e s would appear to be i n .the r a p i d s e p a r a t i o n o f Samarium from Beodymium i n an Y t t r i u m group mixture i n wh i c h t h e s e elements a r e present. I t would a l s o prove an e f f e c t i v e means of s e p a r a t i n g Terbium, Europium and p o s s i b l y G a d o l i n i u m from such a m i x t u r e , G« SUMMARY:. • k p r e l i m i n a r y s t u d y of t h e e f f e c t ' o f c r y s t a l l i s a t i o n o f • i d e n t i c a l m a t e r i a l as t h e b r o i a a t e s , and as the n i t r a t e s has been made. Tiie o r d e r o f s o l u b i l i t i e s of t h e s a l t s i n each s e r i e s d i f f e r s . F o r the r a p i d s e p a r a t i o n of Erbium, o r of Neodj'mium and Samarium front an Y t t r i u m group m i x t u r e the bromates are- t o be recommended f o r t h e p r e l i m i n a r y s e p a r a t i o n . ' ' The n i t r a t e s appear t o o f f e r a s p l e n d i d means, f o r t h e r a p i d c o n c e n t r a t i o n o f Europium, Terbium and G a d o l i n i u m from a g e n e r a l m i x t u r e * (15) 

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